I looked at the game you won- opponent resigned in hopeless position so you therefore won game- if language is the difficulty sometimes i have small ability in French and glad to play if you would like !
How can I know?

In your "Online Chess" page there is an area that looks like this, called My Recent Games...
In the result column you can see that it has won in brackets for the game you've just completed.
In chess if it says 1-0 then white won, if it says 0-1 then black did. If it's a draw you'll just see "draw" there.
How can I know if I win or not a game? It is write "NAME wins by (resignation or something)"?